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From the Galleries: Tycho Brahe's "Astronomiae instauratae mechanica"

By Elana Estrin

Before the telescope was invented, 16th-century Danish astronomer Tycho Brahe built his own instruments to measure star and planetary positions with accuracy up to one arcminute. Brahe described these home-made instruments in his 1602 book, Astronomiae instauratae mechanica, the first edition of which is on display in the Ransom Center’s current exhibition,Other Worlds: Rare Astronomical Works. Mary Kay Hemenway, Research Associate and Senior Lecturer of the Astronomy Department at The University of Texas at Austin, explains why Brahe’s book is one of her favorite items in the exhibition.

The greatest observational astronomer before the use of the telescope is undoubtedly Tycho Brahe. Justly proud of his methods and the many instruments that he designed and had built, he wrote a book illustrating them in 1598—and printed less than 100 copies on his own printing press. The Other Worlds exhibition includes a copy of the first trade edition (1602) that was printed mostly from the woodblocks and plates of the private edition. The book describes his observatory, Uraniborg, on the island of Hven in Denmark and the instruments he used. These instruments measured the altitudes or angular separations between astronomical objects. This allowed him to record carefully the positions of stars, including all of those listed by Ptolemy, and make a large (six-foot) globe of the fixed stars. The most iconic illustration of the book is that of the mural quadrant that allowed the observer to measure the altitude at which celestial bodies crossed the meridian. Its great size is shown by including a life-sized portrait of Brahe himself.

Since Brahe was essentially running a research institute with the equivalent of modern-day students, post-docs, instrument makers, mathematicians who did calculations, technicians, and a library, some of these are shown in the woodcut. We see these assistants in the background—performing observations, working on the data, even doing chemical experiments. Also included are portraits of King Frederick II and Queen Sophia of Denmark—his original patrons—and his faithful dog laying at his feet. It forms a complete picture of the astronomer at work with the components necessary.

Brahe’s observations of comets were so good that they showed that comets moved throughout the solar system, dispelling Aristotle’s notion of “comets as swamp gas that exist in the space between the earth and moon.” Being able to break through the celestial spheres allowed Brahe to come up with an interesting scheme to show the structure of the universe. If we count time by years, he follows Copernicus; his plan allows the Earth to remain in the center of the universe—with the moon and sun revolving around Earth, but the other planets revolving around the sun. His data was essential for Kepler’s development of the laws of planetary motions, but he didn’t live to see the key theoretical idea of his life shot down by the very person he had hired to provide mathematical proof of his unique, Earth-centered theory.